This invention relates to a light-sensitive silver halide photographic material, more particularly to a light-sensitive silver halide photographic material improved in photographic characteristics such as sensitivity, graininess, sharpness, storability and gradation.
Heretofore, as the light-sensitive silver halide photographic material (hereinafter abbreviated as light-sensitive material), development of a light-sensitive material having high sensitivity and finely micropulverized grains has been desired, and a number of improved light-sensitive materials, particularly color light-sensitive materials, have been proposed.
As one of the light-sensitive materials suited for the above object, for example, U.K. Pat. No. 923,045 states that sensitivity can be enhanced without deterioration by applying the same color sensitive silver halide emulsion in separated layers in a high sensitivity silver halide emulsion layer (hereinafter called as high sensitivity emulsion layer) and a low sensitivity silver halide emulsion layer (hereinafter called as low sensitivity emulsion layer) and further by controlling the maximum color forming density at a low level.
In recent years, however, particularly the color light-sensitive material for photography is required progressively to be higher in sensitivity, whereby it is obliged to use coarse silver halide inferior in graininess and/or a coupler with greater coupling speed in the silver halide emulsion layer. For this reason, in the method described in the above U.K. Pat. No. 923,045, the degree of improvement became insufficient, and further elaborations have been done for improvement of graininess.
For example, in Japanese Patent Publication No. 15495/1974, the graininess is stated to be improved by provision of a gelatin layer between the high sensitivity emulsion layer and the low sensitivity emulsion layer. In this method, while graininess at lower density regions can be improved, bad influences on gradation are markedly observed. On the other hand, for restoration of gradation, if sensitivity of the low sensitivity emulsion layer enhanced according to the prior art, for example, by increasing the grain size of silver halide, the graininess in the medium density region which is important particularly in practical technique will unfavorably be deteriorated. Further, in the multi-layer color light-sensitive material having the above constitution, there is also involved the drawback that the color formed image density will be deteriorated in its stability depending on the changes in the developing processing conditions such as pH value, temperature and time.
As another example, Japanese Provisional Patent Publication No. 155536/1982 states that both graininess and gradation can be improved by providing a non-light-sensitive hydrophilic colloid layer between the high sensitivity emulsion layer and the low sensitivity emulsion layer, containing a diffusion resistant coupler for photography which is color formed to substantially the same hue as the diffusion resistant coupler for photography contained in the high sensitivity and low sensitivity emulsion layers, and has a coupling speed not greater than that of the diffusion resistant coupler for photography contained in the high sensitivity emulsion layer. This method involves no failure in gradation and is improved in graininess, but it is not yet satisfactory in improvement in graininess at the regions from low density to medium density. For example, in the above Japanese Patent Publication No. 15495/1974 and Japanese Provisional Patent Publication No. 7230/1978, there is described a method in which a medium sensitivity emulsion layer is provided between the high sensitivity emulsion layer and the low sensitivity emulsion layer and a compound capable of releasing a diffusive developing inhibiting compound (hereinafter called as DIR compound) through the reaction with the oxidized product of a color developing agent is incorporated in said layer. However, these methods have the drawbacks of increased fog accompanying the increased amount of silver halide as well as increase in amounts of valuable silver resources.
Also, in a light-sensitive material having two or more layers of silver halide emulsion layers sensitive to the same color, it is a general practice to improve graininess by making the silver halide emulsion layer having higher sensitivity lower in coupler density (in this case, it appears that the oxidized product of a developing agent formed in the developing reaction will be diffused in a wide scope searching for partners for coupling reaction, thereby forming an unfocused dye cloud with low density without worsening graininess). However, the oxidized product of the developing agent formed by development of the silver halide in said silver halide emulsion layer having higher light sensitivity does not exist only within the layer formed, but will be diffused even to the siler halide emulsion layer having lower light sensitivity to form a dye cloud with conspicuous graininess therein. As the result, when viewing the light-sensitive material, the influence of the developed silver grains in the silver halide emulsion having higher sensitivity will reach even the density (or light-sensitive) region under question, thus ensuing the problem of deterioation of graininess.
Accordingly, an object of this invention is to provide a light-sensitive material having high sensitivity as well as good gradation, further improved in sharpness, image storability and graininess, requiring only a small amount of silver to be employed.